“Just one word…plastics,” a memorable line from the 1967 movie The Graduate, has taken on a whole new meaning. Then, plastics held all the future’s promise. Now, we’ve come to fear them, in part because of the potential health dangers posed by bisphenol A, a chemical found in hard, clear plastics and most cans containing foods or beverages. The spotlight over the past year has been on rigid plastic baby bottles and plastic-lined cans of infant formula. That’s natural, since babies are thought to be most vulnerable to BPA’s reproductive health effects; in animal studies, exposure early in life increased long-term risk of uterine fibroids, endometriosis, decreased sperm counts, and breast and prostate cancer.

It turns out, though, that adults may be at risk, too. A landmark study of more than 1,400 people ages 18 to 74, published today in the Journal of the American Medical Association, found that those with the largest amount of BPA in their urine had nearly three times the risk of heart disease and more than twice the risk of diabetes as those who had the lowest levels. “Even those with the highest BPA levels still had levels way below the currently established ‘safe’ level,” says David Melzer, an epidemiologist at the University of Exeter in England and coauthor of the study. Other researchers say there’s enough evidence from previous animal studies to suggest that BPA is harmful to adults. BPA levels that are slightly elevated but still just one-fifth the safe dose limit established by the Food and Drug Administration trigger an alarming release of insulin in the pancreatic cells of mice–and higher levels lead to pre-diabetes or insulin resistance, says Frederick vom Saal, a biologist at the University of Missouri. BPA also suppresses the release of a hormone from fat cells that normally protects against diabetes and heart disease.